Aeronautics and astronautics – Aircraft structure – Details
Reexamination Certificate
1999-05-05
2001-04-17
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Aircraft structure
Details
C244S208000, C244S209000
Reexamination Certificate
active
06216982
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system for generating a suction air flow for sucking off at least a portion of the boundary layer air flow at least at the flow critical areas on the outer skin of an aircraft, and thereby controlling the boundary layer and particularly a shock boundary layer so as to maintain a laminar boundary layer flow.
BACKGROUND INFORMATION
It is generally known that it is possible to reduce aerodynamic friction resistance and overall drag on the skin of an aircraft, by sucking away at least a portion of the air forming the boundary layer along the aerodynamic surfaces of the outer skin of the aircraft, especially at flow critical areas. Various embodiments and configurations of systems for achieving such boundary layer control by suction are known in the art. For example, German Patent Laying-Out Publication DE-AS 1 280 057 discloses a system for sucking boundary layer air away from an aircraft wing, wherein a suction source located in the interior of the aircraft is connected to the suction passages in the wings by a duct system including suction lines such as pipes or hoses. Details regarding the structure and functioning of the suction source arranged in the interior of the aircraft are not disclosed.
German Patent Laying-Open Publication 197 20 069 and German Patent Laying-Open Publication 196 34 296 each disclose a system for reducing noise emissions and achieving a boundary layer control in connection with a bypass jet engine. One or more hollow air chambers are provided in the nacelle or housing wall of the engine. The outside of the housing wall is provided with corrugations or fluted channels for directing the boundary layer air flow along the housing, and respective openings passing through the housing wall into the hollow chamber from the fluted channels. Further openings pass through the inner wall to connect the hollow chamber or chambers with the bypass channel of the engine.
With such a known structure, at least a portion of the boundary layer air flowing along the outer surface of the engine housing is sucked through the hollow chambers and into the engine bypass channel, as a result of a suction effect created by the supersonic bypass flow being blown through the bypass channel by the fan of the engine. The suction air being sucked through the hollow chambers and into the bypass channel forms a subsonic flow that surrounds the higher velocity active bypass flow and is emitted out of the tail end of the engine together therewith. Thereby, the subsonic flow surrounding or enclosing the supersonic bypass flow is intended to reduce the noise emissions. By also providing a suction flow into the bypass channel upstream of the fan, the flow velocity along the tips of the fan blades is reduced, whereby the forward noise emissions from the fan are intended to be reduced. Both references generally mention that the arrangement of forward-aft extending fluted channels on the outer surface of the engine housing with suction holes therein could also be provided on other surfaces of the aircraft, such as the fuselage and the wings, and that these other surfaces could be pneumatically connected to the suction effect provided by the engine fan in order to achieve a boundary layer control on these surfaces.
German Patent Laying-Open Publication 196 17 952 and corresponding U.S. Pat. No. 5,884,873 (Breit) issued Mar. 23, 1999, disclose a suction generator system including at least one ejector or jet pump for generating a suction flow that is used to suck at least a portion of the boundary layer air through suction holes provided in the aircraft skin. The ejector or jet pump is operated by any selected one or more of several airflow sources, including the pressure differential between the pressurized passenger cabin and the ambient exterior environment, and a flow of high pressure tap or bleed air from at least one engine.
The prior art has not been able to provide an economical and easily adaptable system using one or more suction sources to achieve suction and control of the boundary layer air flow over relatively large surface areas of an aircraft, using the high mass flow of air being moved by an air breathing engine, such as the bypass flow of a high bypass ratio fanjet or turbofan engine, as the primary driving force for the suction generation. Particularly, the prior art solutions have not been shown to achieve an adequate suction flow to provide the required boundary layer control over large surface areas of the aircraft using only the bypass flow of an engine as the driving force for the suction generation. The prior art systems also generally require specialized construction of the aircraft engine or engines, and are not easily retro-fittable in existing aircraft.
SUMMARY OF THE INVENTION
In view of the above, it is the aim of the invention to provide a system for achieving boundary layer control by means of suction in an aircraft, which economically uses the pre-existing energy resources of an air breathing engine, and particularly a modern bypass fanjet or turbofan engine, while providing a sufficient suction air flow to achieve a complete boundary layer control including a shock boundary layer control for large suction areas of the aircraft skin. It is a further object of the invention to provide such a system that is nearly free of maintenance requirements and also reliable and robust against failure, while being adaptable to many different configurations of aircraft, and retro-fittable in existing aircraft engines. The invention also aims to avoid or overcome the additional disadvantages of the prior art, and to achieve further advantages, as apparent from the present specification.
The above objects have been achieved in a boundary layer suction system according to the invention, provided in an aircraft including an aircraft body and an air breathing engine connected to the aircraft body, wherein the aircraft body includes a fuselage and wings for example, and an outer skin of the aircraft body includes suction areas at least at the flow critical areas thereof. The system provides suction at the suction areas to suck away at least a portion of the boundary layer air flow, in order to maintain a proper laminar flow at these critical areas. The system includes at least one jet pump or ejector pump arranged in the open flow cross-section of the engine and a suction conduit that connects the jet pump to at least one of the suction areas of the outer skin of the aircraft. The suction areas are provided with hollow suction passages therein, as well as holes or a porous surface through which the boundary layer air may be sucked away. A driving jet of air being propelled through the engine drives the jet pump in order to generate the required suction.
According to particular embodiments of the invention, the jet pump may include either a simple bent or curved suction pipe terminating in an open, flared outlet mouth or bell facing downstream in the driving jet air flow. Alternatively, the jet pump may include an internal channel or driving jet pipe that conveys the driving jet internally through the jet pump so that it generates the driving suction inside the flared outlet mouth or bell of the suction pipe. The jet pumps are arranged at one or more locations within the engine, namely in the engine intake upstream of the fan, in the bypass channel just downstream of the fan, in the core channel of the engine upstream and/or downstream of the compressor assembly, combustion chamber and turbine assembly, and/or in the bypass channel at a point at which the hot core gases combine with the bypass flow at the tailcone of the engine transitioning to the thrust nozzle.
The inventive system achieves an economical boundary layer suction and control, and/or similarly a shock boundary layer control in an aircraft, by using the pre-existing energy resources of the air breathing engine, which are conventionally not otherwise available. By arranging a number of the jet pumps at suitable locations within the engine according to the invention, it is
Meister Juergen
Pfennig Juergen
DaimlerChrysler Aerospace Airbus GmbH
Eldred J. Woodrow
Fasse W. F.
Fasse W. G.
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